1. Field of the Invention
The present invention is related to a circuit substrate, especially to a high thermal conducting circuit substrate and a manufacturing process thereof.
2. Description of Related Art
In the field of chip packaging technologies, as the thermal generation of chips keeps raising, the carrier, for example, the leadframe or package substrate used for carrying chips, needs to have good thermal dissipation efficiency to lower the temperature of the chips during operation.
Taking the conventional Quad Flat No-lead (QFN) type package as an example, which utilizes a 5-mil-thick copper plate, and patterns the copper plate by etching to form a plurality of bonding pads. Some of the bonding pads are used for chip bonding, while another part of the bonding pads is used for wire bonding. Signal I/O pads on an active surface of the chip are electrically connected with the wire bonding pads through a plurality of wires respectively.
During the process of the QFN type package, a plastic molding process is carried out to form a molding compound encapsulating the chip and the wires and exposing the bottom surfaces of the bonding pads on the bottom of the package after bonding chips to the chip bonding pads and connecting the wire bonding pads with the I/O pads of the chips through the wires. The exposed bottom surfaces of the bonding chips can be directly soldered to a Print Circuit Board (PCB). Thus, the thermal generated during the operation of the chips can be transmitted to the PCB through the chip bonding pads. Hence, in the application of high thermal chip packaging, QFN type packaging body is conducive to transmitting the heat produced by the chips to the PCB, and the molding compound can also completely seal the chips and the circuits.
Additionally, for the package of LED chips, the top of the package has to be open so as to emit the light from the LED chips. Although the QFN type package has a shorter signal transmission path, but the top of the QFN type package is not open for the light penetration, which is why it is hard to apply the QFN type package on LED chips.